The long term goal of this project is to develop an HIV vaccine or vaccine component using genetically detoxified bacterial toxins as vector molecules for induction of CD8+ T cell responses, including cytolytic T lymphocytes (CTL). The candidate vaccine molecules will consist of genetic fusions of HIV antigens with the toxins to stimulate HIV-specific CTL activity and other CD8+ T cell responses in vivo. These toxins enter eukaryotic cells and therefore can delivery antigens for processing and presentation by MHC class I molecules, a complex which is recognized by CD8+ T cells. The toxins to be used are genetically detoxified derivatives of pertussis toxin (PT) and cholera toxin(CT), PT-9K/129G and CT-K63, respectively, which are completely devoid of toxicity but retain other properties. The fusion molecules will be tested in model systems in vitro and in vivo to assess their class I targeting capacity, their immunogenicity in vivo and their protective capacity in an animal model. The specific aims are: (1) To construct detoxified toxin-HIV/SIV antigen fusions that are assembled and secreted efficiently by the bacterial hosts, and to purify these fusion proteins. (2) To demonstrate the CTL- stimulatory capacity of such fusion proteins in vitro, by infection of target antigen presenting cells and CTL lysis assays, and in vivo, by immunization of mice and assay for antigen-specific CTL and other immune responses. (3) To demonstrate the immunogenicity of the fusion proteins in Rhesus macaques and to investigate their protective capacity against challenge with a chimeric simian/human immunodeficiency virus, as a model for HIV infection. One great advantage of this strategy is that it utilizes a vector that, in cone case, is already a vaccine molecule in humans (PT-9K/129G, which is in use as a pertussis vaccine component), and in the other case (CT), is widely used as an adjuvant, particularly for enhancement of mucosal immune responses. These fusions may therefore represent powerful mucosal and systemic vaccine molecules for HIV. This project will complement those in the accompanying proposals which aim to study candidate vaccines designed to stimulate alternative immune responses and will utilize several of the same assays and strategies to test these vaccines. Our fusions may be effective as vaccine molecules either alone or in combination with one of the vaccine candidates described in the accompanying proposals in a prime boost strategy.